Swedish patent specification No. 225,122 discloses an apparatus of the aforesaid kind, wherein the inflowing liquid is divided into split flows. These split flows are caused to pass a great number of small cavities and are accelerated towards a working slot where the processing is performed by cutting, crushing and interparticular grinding, the small particles being subsequently forced through a great number of sonic treatment chambers, wherein the particles in addition to the sonic treatment in the upstream are also subjected to sonic vibrations in the transverse direction. Such an apparatus is relatively complicated, requires much energy and is difficult to clean due to the small cavities, which is an essential drawback, especially when the apparatus is to be used for homogenization of milk or for treatment of other articles of food.
British patent specification No. 1,437,286 discloses an apparatus of a far simpler construction. In this apparatus the liquid, e.g. milk to be homogenized, is simply pumped through a T-tube past an ultrasonic generator surface. This apparatus is admittedly easy to clean, but even with the use of much energy for producing ultra-sound and a small amount of passing liquid, it ensures no product of sufficiently good quality, that is, with practically perfect disintegration and uniform dispersion of the ingredients in the liquid mixture which is homogenized or emulsified. An effective ultrasonic treatment occurs only in the interface of the liquid passing the ultrasonic generator surface. At a slightly greater distance from this interface there is no appreciable emulsification and the ultra-sound has in itself no admixing or kneading effect and thus does not increase the grinding of e.g. the water drops in fuel oil. Since the amounts of liquids pumped past the ultrasonic generator surface at a slightly greater distance have no possibility of being returned and of contacting the surface, this known apparatus permits only of inadequate homogenization or emulsification and insufficient mixing to ensure a uniform dispersion of the ingredients in the liquid, even at a relatively high consumption of energy and with the use of a small amount of passing liquid.